Diabetes Mellitus remains a major health problem, particularly because of the chronic complications affecting large blood vessels (accelerated atherosclerosis, especially in the coronary and cerebral vasculature), and small blood vessels (the microangiopathy of diabetic retinopathy and diabetic renal disease), and numerous metabolic-vascular problems related to the nervous system. It is thought that these chronic complications relate to insufficient metabolic control. Thus, the ultimate project objective is a miniaturized implantable glucose-controlled insulin delivery system. The least defined component of such a system is a miniature implantable glucose sensor. Development of other essential components such as power supplies, microcomputers, a drug reservoir and pump systems will present fewer problems. This program has focused upon an electrochemical glucose sensor utilizing a platinum glucose electrode. Work to date has demonstrated the suitability of high area platinum electrodes operating in the transient controlled potential mode with time-varying potential wave forms. Employing a new technique discovered on this project termed the "compensated net charge method" for analysis of data from potentiodynamic measurements, greatly improved sensitivity, selectivity and reproducibility of glucose measurements has occurred testing solutions containing varying coreactant (amino acids and urea) concentrations. The proposed program builds upon this compensated net charge method and includes improvement of selectivity, measuring glucose in serum ultrafiltrates with varying coreactant concentrations, construction and testing of a prototype sensor, glucose electrode and sensor longevity, design and construction of a prototype electronic package to operate an implantable glucose sensor, and fundamental and exploratory research to understand glucose oxidation on catalytic surfaces and the influence of non-glucose materials.